This invention relates to manually operable pushbutton keyboard systems for electronic pocket calculators, for pushbutton telephones, or for other electrical or electronic appliances, and it is more particularly concerned with such a keyboard which utilizes dished or domed disks as switch actuating elements in momentary single-pole, single-throw (SPST) switches on the keyboard.
Domed disks have been successfully utilized as switch actuating elements in pushbutton keyboard systems in the past. They offer several advantages as they require fewer parts than other types of SPST switches, are readily manufactured, and are easy to assemble. Furthermore, upon depressing the disk to an overcentered actuated position, they provide a tactile feel and an audible snapping sound signalling the operator that the switch has been properly actuated. In prior art keyboards, such as illustrated in the following coassigned U.S. Pat. Nos. 3,684,842, 3,806,673 and 3,808,384, the disks are shown to be retained at their respective switch locations by means of a relatively thick (i.e., having a thickness of about the height of the disk) retainer plate having an array of openings therein for reception of the disks as they are supported above their respective contacts, and by a sheet of insulative material, such as polyethyleneterephthalate, commercially available under the trade designation MYLAR from the E. I. duPont de Nemours and Company. As illustrated in FIG. 4 of the previously mentioned U.S. Pat. No. 3,806,673, this MYLAR sheet has in the past been adhesively bonded to the top face of the retainer plate, but it was free of the outer convex faces of the disks. It has been found that if the MYLAR sheet was adhesively bonded to the outer faces of the disks and to the retainer plate, the MYLAR sheet would grip the outer faces of the disks and hold them in a semi-actuated position which, under some circumstances, would prevent the disks from making contact with their respective contacts when manually depressed by the operator.